Many readers, and surely most Irish readers, will finish this book in a state of white-knuckled rage, mingled with sorrow and at least a pang of guilt. It is a detailed, thoroughgoing and appalling account of the Magdalene laundries, the most famous, and most infamous, among Ireland’s extended and varied landscape of penal or correctional institutions, which operated for most of the 20th century (the last of the laundries was closed in 1996).

As the academic Louise Brangan points out in The Fallen, it is easy to become confused by the number and variety of prisons, mental asylums, orphanages, workhouses and homes for unmarried mothers that proliferated in Ireland between the foundation of the Irish Free State in 1922 and the late 1990s. However, the Magdalene laundries were unique. Dr Brangan writes: “In a regime distinguished by its excessive inhumanity, the Magdalene laundries were its deep end. In 1951, when the laundries were at their height, for every 100,000 males, 27 were in prison … [while] for every 100,000 females, 70 were in a laundry. These were not peripheral: they were Ireland’s main carceral institution.”

The laundries were set up by the state, but run by nuns. The inmates, from girls as young as nine to women in their 80s, worked for no pay, six days a week, laundering, with mostly hand-operated, unwieldy machinery, everything from priests’ vestments and prisoners’ uniforms to the family linen of middle-class homes. Discipline was rigorous, and the smallest transgressions were severely punished. And who were they, these launderer-slaves? “Irretrievable women and girls, the fallen, who were believed to have engaged in sexual misconduct so egregious that they had strayed dangerously, irrevocably, beyond the lines of what was acceptable.”

How did they become enmeshed in this ghastly spider’s web? Some were simply lifted off the streets. In her prologue, Brangan tells of 15-year-old Eileen, “who disappeared on a quiet Sunday evening in February 1954”. Eileen had run away from an abusive family and was working as a maid in a bed-and-breakfast establishment in Dublin. That Sunday evening she was approached at the front desk by two women she had never seen before, and who she learned later were members of the Legion of Mary, a lay organisation with the self-appointed mission, Brangan writes, “to guard Ireland’s moral boundaries”.

The two women drove Eileen to a large, gated house in the suburbs, topped by a metal sign: “Saint Mary Magdalen’s Asylum”. “This was not tucked away, it sat among the row of ordinary local businesses: butcher, dairy, post office, pub, Magdalene laundry.” Here, Eileen was received by a nun, who took away her clothes and gave her an institutional smock, cut off her hair, and changed her name. From now on she would not be “Eileen”, but “60”.

How the two legionnaires knew of Eileen’s existence, we are not told; someone at the lodging house might have “said something”, or a family member might have reported her. What was her transgression? “Irish women and girls did not need to do anything so egregious as become pregnant to be detained in a Magdalene laundry” – the majority of inmates “were no more than the wayward and unwanted; homeless, needy, abused or rejected. It was their very existence that was treated as offensive.”

It is hard now to comprehend the moral climate of 20th-century Ireland, and the level of repression it imposed. Irish travellers to eastern Europe before the fall of the Berlin Wall in 1989 were struck by the sense of familiarity they felt in cities such as Warsaw, Prague or Budapest. The people there, unless they were part of the state apparatus, had the Communist party controlling their lives from the cradle to the grave, while we in Ireland had the Catholic church doing the same thing. As the historian Hugh Trevor-Roper remarked, communism and Catholicism are but two sides of the same coin.

The laundries, standing in plain sight, were largely ignored by a public content to pass those tall, locked iron gates whistling loudly and with eyes averted, in order not to see the mighty fortresses they guarded, or hear the pleas of those held within the granite walls.

Although the laundries were an outrage, they were not the worst of the penal institutions set up by the state and administered by the religious. There were, for instance, the mother and baby homes, through which an estimated 56,000 women and girls passed, and where about 57,000 babies were born, mainly in the 60s and 70s. The most notorious of these institutions was the Bon Secours home in Tuam, County Galway. From 2010 to 2014, a local historian, the quietly heroic Catherine Corless, published newspaper reports of her researches, which revealed that nearly 800 babies were buried in the grounds of the home in an unmarked mass grave that had once been used as a septic tank.

To date, more than €33m in redress payments have been made to survivors of the laundries; the money was provided by the Irish government, while the religious orders have for the most part declined to contribute. At the close of her book, a superb if horrifying testament, Brangan quotes one of the survivors, Carmel, speaking of the legacy left by her time in the laundries: “There’s always something in my life that will remind me of my past life and that’s where I will never get closure, never will. I’ve moved on, yes, I’ve moved on a bit. But I’ll never heal.”